[0001] The present invention relates to brush seals for rotary machines such as steam and
gas turbines and particularly relates to brush seals and labyrinth-brush seal combinations,
as well as to methods for retrofitting brush seals in the flow path of the rotary
machine to provide labyrinth-brush seal combinations.
[0002] Rotary machines, such as steam and gas turbines, used for power generation and mechanical
drive applications are generally large machines consisting of multiple turbine stages.
In turbines, high pressure fluid flowing through the turbine stages must pass through
a series of stationary and rotating components, and seals between the stationary and
rotating components are used to control leakage. The efficiency of the turbine is
directly dependent on the ability of the seals to prevent leakage, e.g., between the
rotor and stator. Turbine designs are conventionally classified as either impulse,
with the majority of the pressure drop occurring across fixed nozzles, or reaction,
with the pressure drop more evenly distributed between the rotating and stationary
vanes. Both designs employ rigid tooth, i.e., labyrinth, seals to control leakage.
Traditionally, rigid labyrinth seals of either a hi-lo or straight shaft design are
used. These types of seals are employed at virtually all turbine locations where leakage
between rotating and stationary components must be controlled. This includes interstage
shaft seals, rotor end seals, and bucket (or blade) tip seals. Steam turbines of both
impulse and reaction designs typically employ rigid, sharp teeth for rotor/stator
sealing. While labyrinth seals have proved to be quite reliable, their performance
degrades over time as a result of transient events in which the stationary and rotating
components interfere, rubbing the labyrinth teeth into a "mushroom" profile and opening
the seal clearance.
[0003] Another type of seal used in many environments, including rotary machines, is a brush
seal. Brush seals are generally less prone to leakage than labyrinth seals. A brush
seal can also accommodate relative radial movement between fixed and rotational components,
for example, between a rotor and a stator, because of the flexure of the seal bristles.
Brush seals also generally conform better to surface non-uniformities. The result
of using brush seals is better sustained rotary machine performance than is generally
possible with labyrinth seals.
[0004] In accordance with a preferred embodiment of the present invention, there is provided
a combination or hybrid labyrinth-brush seal in the environment of a rotary machine
such as a turbine. Brush seals
per se have generally applicability to rotary machines and can be used in lieu of labyrinth
seals. Brush seals are advantageous in that context and provide improved sealing,
while occupying considerably less axial space as compared with conventional labyrinth
seals. As a result, more compact rotary machine, e.g., turbine, designs can be realized.
Alternatively, by employing brush seals, the span that would normally be occupied
by labyrinth teeth can be used to allow additional turbine stages, resulting in increased
turbine efficiency. As a further advantage, application of brush seals at end packing
locations can reduce leakage to the point that the need for a gland sealing/exhauster
system, for example, in a steam turbine, is eliminated. At rotor end seals, it is
also possible to use brush seals in conjunction with face seals. Further, in certain
steam rotary machine applications, some leakage is desirable for cooling of components
such as rotors. At these locations, brush seals can be used in conjunction with orifices
or other flow bypass mechanisms to ensure that the proper amount of leakage is obtained.
[0005] A typical brush seal for use in the present invention comprises a bristle pack, i.e.,
bristles sandwiched between two metallic plates. The bristles are generally alloy
steel wires, drawn to a diameter of 0.002-0.006 inches, although the exact diameter
depends on the specific seal application. Larger wire diameters are used for seals
exposed to a high pressure differential between the upstream and downstream sides.
The backing (downstream) plate prevents the bristles from deflecting axially under
pressure load. As a result, fence height (h) is a critical design variable. Fence
height is the distance the bristles extend freely from their support, i.e., the distal
end of the support plate, to their free ends, which typically are in engagement with
the rotating part. For a steam turbine application, where the expected maximum radial
rotor deflection is approximately 0.040 inches, the fence height must therefore be
a minimum of 0.040 inches. Fence heights vary significantly, particularly in gas turbines,
depending on the seal location, from 0.030 for bearing seals, to 0.120 for high pressure
packing seals to 0.300 for turbine interstage seals. The forward (upstream) plate
holds the bristles in place during seal fabrication.
[0006] During shaft radial excursions, the bristles must be able to temporarily deflect
without buckling. In order to accommodate these excursions, the bristles are not oriented
in a perfectly radial direction, but are instead canted at some angle. Typically,
this angle is between 45 and 60 degrees. Increased angles are used to allow for increased
radial shaft excursions.
[0007] In accordance with one aspect of the present invention, brush seals are combined
with labyrinth seals and may be supplied as original equipment or retrofitted into
an existing labyrinth seals. Thus, the brush seal may be provided between adjacent
labyrinth teeth or at one or both ends of the seal or at various one or more locations
between the teeth and at one or both ends of the seal. Advantageously, one of the
labyrinth seal teeth may be used as a backing plate for each brush seal. This allows
the brush seal to be incorporated into the labyrinth seal with a minimal loss, if
any, of labyrinth teeth, and results in a highly fail-safe design. In addition, the
tapered shape of the labyrinth tooth provides an anti-hysteresis quality to the brush
seal. Hysteresis occurs when the seal is exposed to a large pressure differential,
followed by a large relative radial movement which deflects the bristles. Friction
forces acting on the bristles prevent them from returning to their steady-state positions
until they are relieved of the large pressure load. By providing a tapered shape to
the bristle backing structure, the normal force on the backing plate is reduced and
the hysteresis tendency is abated.
[0008] A second method of providing anti-hysteresis capability to the brush seal is to coat
the upstream surface of the backing plate with a material that has an extremely low
coefficient of friction such as, for example, boron nitrate. Thus, the friction force
is reduced by reducing the friction coefficient rather than the normal force.
[0009] By combining brush seals with conventional labyrinth seals, a fail-safe seal is advantageously
created. The brush seal provides essentially all of the sealing capability as long
as it remains intact. However, if it becomes damaged or worn, the adjacent labyrinth
teeth provide sufficient sealing to enable the rotary machine, e.g., a turbine, to
be operated until its next scheduled maintenance outage. The brush seals may be welded
in place, or they may be mechanically fastened, e.g., by using bolts. Particularly
advantageous is that brush seals can be retrofit on existing rotary machines to provide
a combination labyrinth-brush seal with a minimum of modification to the extant labyrinth
seal teeth. For example, a brush seal may be disposed between a pair of plates with
one plate having a tongue-and-groove fit for fitting the brush seal to a labyrinth
seal ring, e.g., on an end face thereof, with the brush seal being finally welded
directly to the labyrinth seal ring. Alternatively, a circumferential groove may be
machined in the labyrinth seal ring between adjacent teeth or at the seal ring ends.
It will be appreciated that the groove may necessitate removal of one or more teeth
of the labyrinth seal but this can be accomplished without deleterious effect on the
performance of the resulting combination seal. The brush seal may then be slid into
place and welded along the inner diameter of the interface. The brush seal backing
plate may also have a profile similar to that of a labyrinth tooth, or may use an
existing tooth of the labyrinth seal, resulting in a fail-safe design.
[0010] It will be appreciated that labyrinth seals in certain rotary machines, such as steam
turbines, are generally segmented, with between four and eight individual segments
forming the entire 360 degree seal. Each segment is held in place independently, and
can typically move radially independent of the other segments. As a result, the brush
seal for retrofitting in a given labyrinth seal of a steam turbine is also fabricated
in sections, each section being fastened to a single labyrinth seal segment.
[0011] In most steam turbines, the labyrinth seal segments are "spring-backed." That is,
they are held in place by sprung steel strips, and are free to move radially when
subjected to severe rotor/seal interference. By attaching individual brush seal segments
directly to the labyrinth seal segments, the brush seals are also provided with this
"spring-backing" protection in the event of severe rotor rubs.
[0012] Also sometimes employed in steam turbines are springs for maintaining the labyrinth
seal segments positioned radially away from the rotor. A cavity is also located on
the backside of the segments which can be pressurized to close the seals to the design
clearance, after the rotor has been brought to speed and any severe transients have
passed. Retrofitting brush seal segments to the labyrinth seals in such an arrangement
maximizes the wear life of the brushes, since the seals are not subjected to the most
severe rotor/stator interferences that occur during turbine start-up and shut-down
cycles.
[0013] In order to survive in a steam turbine environment, brush seals must be designed,
e.g., to withstand pressures up to 3500 psig and temperatures ranging from ambient
to approximately 1050°F. In addition, the steam seals must be sufficiently robust
to withstand relative radial excursions of at least 0.040 inches. Seal diameters generally
range from approximately 6 inches to 30 inches for shaft seals, and 30 inches to 60
inches for bucket tip seals. Rotor speed ranges from 1500 to 7500 RPM or higher.
[0014] In order to survive in a gas turbine environment, brush seals must be designed to
withstand pressures up to 200 psia and temperatures ranging from ambient to approximately
1500°F. In addition, the seals must be sufficiently robust to withstand relative radial
excursions ranging from 0.030 to .0300", depending on location. Seal diameters generally
range from approximately 40 to 60" for high pressure packing seals, 15 inches to 25"
for bearing seals, 35 to 70" for turbine interstage seals, and 40 inches to 120" for
blade tip seals. Rotor speed ranges from 1500 to 4500 rpm.
[0015] Traditionally, brush seals have been utilized in conjunction with shafts that have
been coated with a chrome carbide coating, to improve wear resistance. In order to
make brush seals more economically feasible in steam and gas turbines, they can be
applied to uncoated surfaces, with acceptable wear rates of both the seal and shaft.
Typically, the wear pair for a brush seal on a steam turbine rotor consists of a cobalt
alloy bristle material (such as Haynes 25) contacting a rotor surface of either CrMoV
(for the shaft) or 12Cr (for bucket tips). Rotor materials such as Inconel 718 are
possible on newer gas turbines. The shaft geometry can also be designed to mitigate
wear by taking advantage of relative axial motion. If the radial interference occurs
at a location other than that where the brush seal is located at steady state operation,
the shaft can be grooved to decrease the interference.
[0016] An important consideration in the design of brush seals for turbines is the pressure
differential across the seal. Whenever possible, it is desirable to employ brush seals
that consist of a single row of bristles. However, in order to accommodate the radial
shaft excursions expected in a steam turbine, as well as the high pressure drop that
occurs at some turbine stages, it is sometimes necessary to employ brush seals consisting
of two or more bristle packs in series. In multiple-stage brush seals, it is common
for flow leaking beneath the upstream bristle pack to induce a vortex between the
bristle packs, and for this vortex to be damaging to the following row of bristles.
Specifically, the vortex can be such that the flow on the upstream side of the second
row of bristles is radially outward, tending to pull the bristle pack apart and damaging
the seal. To prevent this phenomenon from occurring in a gas turbine, according to
the present invention, a radial step may be provided in the rotor between the two
bristle packs with the two bristle packs lying at the two different diameters. With
appropriate axial location of the rotor step, this arrangement results in a reversal
of the flow direction at the upstream edge of the second bristle pack. Such a seal,
in which the flow is radially inward along the bristles, is very effective.
[0017] In a steam turbine, however, the large relative axial movements that take place between
the rotor and stator during transients preclude use of rotor steps as a method of
preventing flow-induced damage of multiple stage brush seals. Instead, the pair of
bristle packs may be axially separated by a section of conventional labyrinth teeth
and the downstream bristle pack is thus virtually unaffected by the presence of the
upstream bristle pack. In a turbine seal that normally consists of two or more labyrinth
rings, one single stage brush seal can be retrofit into each of the labyrinth seal
rings, resulting in an effective two or multi-stage brush seal. An additional advantage
to this arrangement is that it is a fail-safe design. That is, if the brush seal should
fail for any reason, the labyrinth seal is still present, and will provide sufficient
sealing for the turbine to operate until its next scheduled maintenance outage.
[0018] The combination labyrinth-brush seal described herein is applicable in steam turbines
to bucket tip seals, shaft seals, and spill strips. For example, a brush seal may
be retrofit to a labyrinth seal ring at the tip of a steam turbine rotating bucket
using the tongue-and-groove geometry or a grooved arrangement previously described.
The brush seal can be mounted at any axial location along the labyrinth seal ring,
and can be either welded in place or fastened mechanically. In addition to the relative
radial rotor/stator movements that the shaft seals must withstand, bucket tip seals
must endure any surface discontinuities that exist between individual buckets or bucket
covers and the stator which makes the combined labyrinth-brush seal hereof ideal for
that purpose.
[0019] In addition to the bucket tip seals, root radial spill strips may also employ the
labyrinth-brush seal combination. Any of the mounting arrangements discussed earlier
for combination seals are also applicable to the spill strip seals. Again, a fail-safe
seal is provided by mounting the brush seal in tandem with a labyrinth seal including
providing the brush seal backing plate with a labyrinth tooth profile in an original
equipment seal, or utilizing an existing labyrinth tooth as the backing plate.
[0020] Significantly, the labyrinth-brush seal combinations described here are applicable
to impulse turbines, as well as reaction turbines. Impulse turbines are generally
of a wheel and diaphragm construction, while reaction turbines generally utilize what
is commonly referred to as a drum rotor. For application to reaction turbines with
drum rotors, the brush seals may be attached to the inner surface of the stationary
blades in combination with the existing labyrinth seals or installed as original equipment.
For both turbine designs, it is also possible to attach the brush seals to the rotating,
rather than the stationary, components.
[0021] The brush seals themselves can either be in a ring form or the seals can be fabricated
in a linear sense. The fabricated seals can be in the form of an "L" shape, a "T"
shape, or a "Y" shape down the linear length of the fabricated seal. When the linear
sealing strip (regardless of its cross-section shape) is needed, it can be "rolled"
into a given diameter and cut into various segments. This rolled and segmented seal
can then be similarly joined to the steam turbine seal elements in the same fashion.
This linear seal overcomes the requirement for having new tooling for each different
seal diameter required in the steam turbine. Since there are thousands of different
sealing diameters across the steam turbine product line, the result of the linear
seal is a considerable reduction in tooling cost. The fabricated and rolled linear
seal can be provided with "extra" material on its sheet metal components, so that
the cross section may be machined to fit the seal into slots.
[0022] On seals where multiple segments (arcs) are needed, the hot end-gap clearance between
each seal segment becomes a major source of the greatly reduced leakage of the combined
labyrinth-brush seal or labyrinth-fabricated linear brush seal. To further control
this leakage, a tightly rolled-up section of the same cloth utilized in fabricating
the linear seal may be spot welded or affixed to the segment end. As the segments
are brought to operating temperature, they will grow together, crushing the tightly
rolled cloth and thereby vastly reduce the gap leakage. The overall seal performance
will thus be greatly improved.
[0023] In a preferred embodiment according to the present invention, there is provided in
a rotary machine having a rotatable component and a component fixed against rotation,
the components lying about a common axis, and a labyrinth seal between the components
including at least one generally circumferentially extending tooth carried by one
of the components and projecting generally radially toward the other of the components
to effect a seal therebetween, a method of forming a combination labyrinth and brush
seal between the components, comprising the steps of retrofitting a circumferential
array of discrete bristles on the one component axially adjacent the one tooth by
securing the array to the one component with the bristles lying in a plane generally
normal to the axis and with the distal ends thereof projecting toward the other component
beyond the radial extent of the one tooth for substantial sealing engagement with
the other component.
[0024] In a further preferred embodiment according to the present invention, there is provided
a rotary machine comprising a rotatable component, a component fixed against rotation,
the components lying about a common axis, a labyrinth seal between the components
including a plurality of axially spaced circumferentially extending teeth carried
by one of the components and projecting radially toward the other of the components
to effect a labyrinth seal therebetween, a brush seal between the components, including
a circumferential array of discrete bristles carried by the one component for disposition
axially adjacent at least one of the teeth, and means for securing the array of bristles
to the one component with the bristles lying in a plane generally normal to the axis
and with the distal ends thereof projecting toward the other component beyond the
radial extent of the teeth for substantial sealing engagement with the other component.
[0025] In a still further preferred embodiment according to the present invention, there
is provided a labyrinth seal for a rotating machine comprising a plurality of axially
spaced and radially extending teeth and at least one circumferential array of discrete
bristles projecting beyond the radial extent of the teeth.
[0026] In a still further preferred embodiment according to the present invention, there
is provided a method of effecting sealing in a rotating turbomachine having a labyrinth
packing with multiple rows of axially spaced circumferentially extending seal teeth
to prevent fluid flow between rotating and stationary components thereof, comprising
the step of replacing at least one tooth with a brush seal.
[0027] In a still further preferred embodiment according to the present invention, there
is provided a method of repairing a segment of toothed labyrinth packing for a turbomachine
comprising the step of replacing at least one tooth with a brush seal.
[0028] Accordingly, it is a primary object of the present invention to provide novel and
improved brush seals and combination labyrinth-brush seals for sealing between fixed
and rotating components of rotating machinery and methods of retrofitting existing
rotating machinery with brush seals to effect fail-safe combination labyrinth-brush
seals.
[0029] Embodiments of the invention will now be described, by way of example, with reference
to the accompanying drawings, in which:-
FIGURE 1 is a schematic illustration of a sealing ring segment illustrating a labyrinth
seal about a rotor;
FIGURE 2 is a schematic illustration of a labyrinth seal between a sealing ring segment
and the covers for buckets or blades of a rotating component;
FIGURE 3 is a schematic illustration of a turbine wheel illustrating a labyrinth seal
between the wheel and a fixed component of the turbine;
FIGURE 4 is an end elevational view of a segmented brush seal;
FIGURE 5 is an enlarged cross-sectional view thereof taken generally about on line
5-5 in Figure 4;
FIGURE 6 is a fragmentary cross-sectional view illustrating a combined labyrinth-brush
seal according to the present invention;
FIGURE 7 is an enlarged view of a form of brush seal employed in the present invention;
FIGURES 8 and 9 are schematic illustrations illustrating a combined labyrinth-brush
seal of the present invention between sealing ring segments and a rotor;
FIGURE 10 is a schematic illustration of axially spaced brush seals in engagement
with a rotor;
FIGURE 11 is a view similar to Figure 10 illustrating the axially spaced brush seals
in conjunction with a stepped rotor;
FIGURE 12 is a view similar to Figure 10 illustrating the combined labyrinth-brush
seal hereof with the brush seals at opposite ends of the sealing ring segments;
FIGURE 13 is a schematic illustration of a multi-stage combined labyrinth-brush seal
according to the present invention;
FIGURE 14 is a schematic illustration of a combined labyrinth-brush seal according
to the present invention between the stator and cover for rotating buckets; and
FIGURES 15A, 15B and 15C are schematic illustrations of a further form of a brush
seal rotor combination in accordance with the present invention.
[0030] Referring now to the drawing figures, particularly to Figure 1, there is illustrated
a portion of a rotary machine, for example, a steam turbine, having a turbine shaft
10 disposed in a turbine housing 12 and which shaft 10 is supported by conventional
means, not shown, within turbine housing 12. A labyrinth seal, generally designated
14, between the rotating shaft 10 and the stationary housing 12, includes a seal ring
16 disposed about shaft 10 separating high and low pressure regions on axially opposite
sides of the ring. It will be appreciated that while only one seal 16 is disclosed,
typically multiple-stage labyrinth seals are provided about rotor shafts. Each seal
ring 16 is formed of an annular array of a plurality of arcuate seal elements 18 having
sealing faces 20 and a plurality of radially projecting, axially spaced teeth 22.
The teeth are of a hi-lo design for obtaining close clearances with the radial projections
or ribs 24 and the grooves 26 of the shaft 10. The labyrinth seal functions by placing
a relatively large number of barriers, i.e., the teeth, to the flow of fluid from
a high pressure region to a low pressure region on opposite sides of the seal, with
each barrier forcing the fluid to follow a tortuous path whereby pressure drop is
created. The sum of the pressure drops across the labyrinth seal is by definition
the pressure difference between the high and low pressure regions on axially opposite
sides thereof. These labyrinth seal ring segments are typically spring-backed and
are thus free to move radially when subjected to severe rotor/seal interference. In
certain designs, the springs maintain the seal ring segments 16 radially outwardly
away from the rotor, for example, during startup and shutdown, with fluid pressure
being supplied between the seal ring segments and the rotor housing to displace the
seal ring segments radially inwardly to obtain a lesser clearance with the rotor,
i.e., close the seals, after the rotor has been brought up to speed.
[0031] Figure 2 illustrates a similar arrangement of a labyrinth seal employed at the tip
of the rotating blades or turbine buckets for the rotating machine. Thus, in Figure
2, the labyrinth seal teeth 22a lie in sealing relation to a bucket cover 30 formed
on one or more turbine buckets 32. The principal of operation of the labyrinth seal
at this location is similar as described above.
[0032] Figure 3 illustrates a typical honeycomb-type labyrinth seal, for example, in a gas
turbine. The labyrinth seal teeth 22b are mounted on the rotor wheel 33 and lie in
radial opposition to a honeycomb structure 34 forming part of the stator. Thus, it
will be appreciated that the labyrinth seal teeth may be disposed on the rotating
component of the rotary machine.
[0033] Referring now to Figures 4 and 5, a typical brush seal, generally designated 36,
includes a plurality of bristles 38 extending generally in a radial direction and
which bristles 38 are disposed or sandwiched between a pair of seal plates 40 and
42. The bristles are generally formed of alloy steel wire drawn to a diameter of 0.002-0.006
inches, although larger-diameter wires for use in higher pressure environments may
be used. From a review of Figure 5, it will be seen that the backing plate 42 prevents
deflection of the bristles 38 under the loading from an upstream direction of the
flow, while the distal ends of the bristle project from the distal edge of the plate
42 to engage the opposite component, e.g., the rotating shaft or wheel of a rotary
machine. The bristles 38 are preferably welded between the plates 40 and 42. Additionally,
it will be seen from a review of Figure 4 that the bristles and plates are provided
in segments about the circumference of the axis of the rotating machine.
[0034] Referring to Figure 5, the bristles project from the distal end of backing plate
42 a distance h which corresponds to the maximum deflection of the rotor in a radial
direction. Consequently, the distance h must be a minimum corresponding to that maximum
deflection and is dependent on the expected relative radial deflection for the specific
machine and seal location. It may be on the order of 0.040 inches. Note also that
the upstream plate 40 is useful for maintaining the bristles in place during seal
fabrication, although plate 40 is not necessary to the seal when in use if axial space
is at a premium. It will also be noted in Figure 4 that the bristles 38 extend along
paths which are misaligned with the radius of the rotary machine. Thus, the bristles
extend at an angle, preferably a common angle of approximately 45-60° to accommodate
radial excursions of the shaft whereby the bristles may deflect without buckling.
[0035] In accordance with one embodiment of the present invention, there is provided a combination
labyrinth-brush seal. For example, in Figure 6, the combination seal is illustrated
with the brush seal lying at and along the axially upstream end of the sealing ring
segment 16c with the teeth 22c of the labyrinth seal being located downstream of the
brush seal 36c. In the illustrated embodiment, the bristles 38c of the brush seal
36c are disposed between an upstream clamping plate 40c and an end wall of the sealing
ring segment 16c. The bristles may be secured, for example, by welding. Significantly,
in the illustrated arrangement, one of the labyrinth teeth 22c may be employed as
the backing plate on the downstream side for the bristles 38c of the brush seal 36c.
Consequently, with only the addition of an end sealing plate 40c and without the loss
of one or more of the labyrinth teeth, the fail-safe combination labyrinth-brush seal
may be provided. In the event that the axial spacing is such that no axial increase
in dimension is permitted, one or more of the labyrinth teeth 22c may be removed to
accommodate securement of the brush seal 36c without increasing the axial dimension
of the seal ring segment 16c. This results in a highly fail-safe design wherein, should
the brush seal fail, the labyrinth teeth remain effective to provide a seal. Also,
the downstream backing surface for the bristles 38c of the brush seal 36c may be tapered
to provide anti-hysteresis qualities to the brush seal. By providing the tapered shape
to the downstream backing for the bristles, the normal force on the backing plate
is reduced and the hysteresis tendency is abated. In retrofitting a brush seal to
an existing labyrinth seal segment in a rotating machine, the taper of the teeth of
the labyrinth seal provides that anti-hysteresis quality when the existing teeth are
employed as the backing plate for the additional seal. Alternatively, to provide these
anti-hysteresis qualities, a low-friction coating material 44 such as boron nitrate,
for example, may be provided on the upstream surface of the downstream backing plate
or the upstream surface of the backing teeth of the labyrinth seal to reduce the friction
force. This is illustrated in Figure 7, wherein a backing plate 42d for the brush
seal 36d is provided with the low coefficient material 44.
[0036] Figures 8 and 9 illustrate different embodiments of the combination labyrinth-brush
seal of the present invention. In Figure 8, a brush seal 36e is provided on the upstream
face of the sealing ring segment 16e using a tongue-and-groove fit between the backing
plate 42e of the brush seal 36e and the upstream end face of the seal ring segment
16e. The brush seal 36e may be welded to the segment 16e or mechanical fasteners such
as bolts may be used. In retrofitting a brush seal to a labyrinth seal of this type,
it will be appreciated that an axial extent of the end face of the seal ring segment
16e can be removed such that the brush seal 36e can be applied to form the combined
labyrinth-brush seal combination hereof on seal ring segment 16e with the same resulting
axial dimension as the previous labyrinth seal. As explained previously, where necessary,
one or more of the end labyrinth seal teeth can be removed during this retrofit without
substantial loss of sealing performance, particularly since the brush seal forms the
more effective seal of the labyrinth-brush seal combination. If the brush seal fails,
an effective seal using the remaining labyrinth teeth is still provided.
[0037] Referring to Figure 9, the seal ring segment 16f may be provided with a central groove
46 along its inner face. For example, the groove 46 may be machined in the labyrinth
seal ring as original equipment or during retrofit. The seal ring, for example, as
illustrated in Figure 3, can then be disposed and secured, for example, by welding
in the groove. Thus, the brush seal 36f lies generally intermediate the labyrinth
seal teeth 22f of the combination labyrinth-brush seal. It will be appreciated that
the embodiments illustrated in Figures 8 and 9 may be spring-backed for radial movement
and be of the positive pressure variable clearance type, for example, as disclosed
in U.S. Patent No. 5,002,288 of common assignee, the disclosure of which is incorporated
herein by reference. Alternatively, the sealing ring segments may be of the type described
in U.S. Patent No. 5,375,068, of common assignee herewith, and which disclosure is
also incorporated herein by reference.
[0038] Referring now to Figure 10, it is often desirable to provide brush seals 36g in series
between the rotating and fixed components to accommodate radial shaft excursions and
the pressure drop across the seal. As illustrated in Figure 6, two brush seals 36g
are disposed at opposite ends of a fixed part to effect the seal. As explained previously,
the fluid leakage between the upstream bristle pack induces a vortex between the bristle
packs which may cause damage to the downstream bristle pack. To prevent this phenomena,
a radial step in the rotor can be provided wherein the bristle packs 36h at opposite
ends of the seal lie at different elevations, i.e., radial positions as illustrated
in Figure 11. With the bristle packs 36h at two different diameters as illustrated,
the flow on the downstream bristle pack, rather than being radially outwardly and
tending to pull the bristle pack apart and damaging the seal, is radially inwardly
along the upstream edge of the downstream bristle pack, thus preventing damage to
the downstream bristle pack. This is particularly effective in gas turbines.
[0039] In a steam turbine, it is often not feasible to provide a rotor step to take advantage
of the reversed vortex flow and hence avoid damage to the downstream bristle pack.
However, by separating the upstream and downstream bristle packs by labyrinth teeth
22i as illustrated in Figure 12, the downstream bristle pack 36i is virtually unaffected
by the presence of the upstream bristle pack 36i.
[0040] Consequently, bristle packs may be disposed along opposite axial ends of individual
sealing ring segments or, as illustrated in Figure 13, the bristle packs 36j may be
disposed in multi-stage sealing segments at either the ends of the segments or intermediate
their axial extent as illustrated. It will be appreciated that the bristle packs with
the labyrinth seal teeth may be provided as original equipment or as a retrofit using
the tongue-and-groove arrangement illustrated in Figure 8 or the groove arrangement
illustrated in Figure 9.
[0041] Referring to Figure 14, the combination labyrinth-brush seal hereof may be employed
at the tip of a rotating blade or bucket. Thus, the brush seal 36k may be applied
to an axial end of a sealing strip 48 mounting labyrinth seal teeth 22k for sealing
with the bucket cover 50 of bucket 52. It will be appreciated that the end mounting
of the brush seal 36k can be replaced by a grooved mounting of the brush seal 36k
intermediate axially adjacent teeth similarly as illustrated in Figure 9. As noted
previously, the brush seal can be secured by welding or by mechanical means and can
be provided as original equipment or as a retrofit.
[0042] Figure 14 also illustrates a labyrinth seal tooth 221 adjacent the root of the turbine
bucket or vane 52. This labyrinth tooth 221 forms a root radial spill strip seal 49.
A brush seal, as previously described, may be provided at this location within the
rotary machine similarly as in the previous embodiments by mounting the brush seal
in tandem with the labyrinth seal, providing the brush seal backing plate with a tapered
profile or applying a low coefficient of friction material thereto or utilizing an
existing labyrinth tooth as the backing plate.
[0043] Referring now to Figure 15, in certain instances, particularly in gas turbines, the
rotating part can be particularly designed to mitigate wear on the brush seal. For
example, as illustrated in Figure 15, if the radial interference occurs at a location
other than where the brush seal is located at steady-state operation, the shaft 10m
may be provided with a groove 51 to decrease the interference. Thus, in Figure 15A,
the brush seal 36m is illustrated in a cold position bearing against a rotor of a
certain diameter at an axial location spaced from groove 51. In Figure 15B, the steady-state
location of the brush seal is illustrated vis-a-vis the larger diameter portion of
shaft 10m adjacent the rotor groove 51. In Figure 15C, the shutdown position of the
rotor and brush seal is illustrated, with the brush seal tips engaging in the groove.
It will be appreciated that this form of the invention can be used with or without
the labyrinth seal teeth.
[0044] It will be appreciated that existing toothed labyrinth seals may be retrofitted or
repaired by replacing one or more teeth with brush seals in accordance with the present
invention.
1. A method of forming a combination labyrinth and brush seal between components of a
rotary machine having a rotatable component and a component fixed against rotation,
said components lying about a common axis, and a labyrinth seal between said components
including at least one generally circumferentially extending tooth carried by one
of said components and projecting generally radially toward the other of said components
to effect a seal therebetween,
the method comprising the steps of retrofitting a circumferential array of discrete
bristles on said one component axially adjacent said one tooth by securing said array
to said one component with the bristles lying in a plane generally normal to said
axis and with the distal ends thereof projecting toward said other component beyond
the radial extent of said one tooth for substantial sealing engagement with said other
component.
2. A method according to Claim 1 including installing said array of bristles axially
against an upstream side of said one tooth.
3. A method according to Claim 1 including disposing said array of bristles between a
pair of plates and in multiple layers thereof in an axial direction, said one component
comprising said component fixed against rotation, and securing said plates to an end
face of said one component.
4. A method according to Claim 1 wherein said labyrinth seal includes a plurality of
generally circumferentially extending axially spaced teeth carried by said one component
and projecting radially toward said other component, said one component comprising
said component fixed against rotation, and including disposing said array of bristles
in multiple layers thereof in an axial direction and on said one component intermediate
an adjacent pair of said teeth.
5. A method according to Claim 1 wherein said labyrinth seal includes a plurality of
generally circumferentially extending axially spaced teeth carried by said one component
and projecting radially toward said other component, said one component comprising
said component fixed against rotation, and including removing at least a portion of
one of said teeth and replacing said removed tooth portion with said array of bristles.
6. A method according to Claim 1 wherein said machine comprises a steam turbine including
a fixed housing, said one component comprising a plurality of arcuate segments carried
by said fixed housing for movement in radial directions toward and away from said
axis, at least one spring for each segment biasing said segment for movement in one
of said radial directions, at least one tooth being carried by an arcuate inner face
of each said segment and including the step of securing arcuate sections of said array
of bristles to said segments, respectively, at an axially spaced position along said
segments relative to said teeth.
7. A method according to Claim 6 including forming a groove in an inner face of each
said segment, disposing an arcuate section of said array of bristles between a pair
of arcuate plates and securing said bristles and plates in said grooves of said segments.
8. A method according to Claim 6 including the step of securing a first array of arcuate
sections of said circumferentially extending array of bristles to said segments adjacent
a side thereof upstream of said teeth and securing a second array of arcuate sections
of said circumferentially extending array of bristles to said segments adjacent an
opposite side thereof downstream of said teeth whereby said teeth lie axially between
said first and second arrays of bristles.
9. A rotary machine comprising:
a rotatable component;
a component fixed against rotation;
said components lying about a common axis;
a labyrinth seal between said components including a plurality of axially spaced circumferentially
extending teeth carried by one of said components and projecting radially toward the
other of said components to effect a labyrinth seal therebetween;
a brush seal between said components, including a circumferential array of discrete
bristles carried by said one component for disposition axially adjacent at least one
of said teeth; and
means for securing said array of bristles to said one component with the bristles
lying in a plane generally normal to said axis and with the distal ends thereof projecting
toward said other component beyond the radial extent of said teeth for substantial
sealing engagement with said other component.
10. A method of effecting sealing in a rotating turbomachine having a labyrinth packing
with multiple rows of axially spaced circumferentially extending seal teeth to prevent
fluid flow between rotating and stationary components thereof, comprising the step
of replacing at least one tooth with a brush seal.